Air-bag-use non-coat base cloth and air-bag-use fiber

ABSTRACT

A base fabric for non-coated air bags, in which both the warp and the weft or either of them comprise synthetic fiber multifilaments of flattened cross-section monofilaments having a degree of flatness of from 1.5 to 8.0 and having a monofilament fineness of at moat 10 dtex and a total fineness of from 200 to 1000 dtex, and which satisfies all the following (1) to (3):  
     (1) its cover factor falls between 1700 and 2200;  
     (2) its air permeability under low pressure, P L , is at most 0.1 cc/cm 2 /sec; and  
     (3) its air permeability under high pressure, P H , is at most 20 cc/cm 2 /sec, has high tenacity and low air permeability necessary for air bags and is compactly foldable to save the housing space for it.

[0001] The present invention relates to a base fabric for non-coated airbags, and to fibers for air bags. More precisely, the invention relatesto a base fabric for high-pressure inflatable, non-coated air bags,which has high tenacity and low air permeability necessary to air bagsand which can be compactly folded and housed, and relates to fibers togive the base fabric for such air bags.

BACKGROUND ART

[0002] At present, air bags are indispensable for ensuring the safety ofdrivers and passengers in automobiles, and the percentage of air baginstallation in automobiles is increasing.

[0003] Various matters are required for air bags, which are, forexample, low air permeability for ensuring smooth inflation incollision, high tenacity for preventing the bags themselves from beingdamaged and broken, and flexibility for protecting drivers andpassengers from being scratched on their faces by inflated air bags. Theother important matters for air bags are that the base fabric for themis compactly foldable so as to be housed in a limited small space, andis inexpensive.

[0004] Base fabrics for air bags are grouped into two types, coated basefabrics and non-coated base fabrics. For the former, woven fabrics arecoated with resin; and for the latter, woven fabrics are directly usedas they are. In general, coated base fabrics are said to be advantageousfor ensuring the above-mentioned low air permeability for air bags.

[0005] Many techniques have heretofore been disclosed for realizing airbags that are compactly foldable to save the necessary housing space,not interfering with high tenacity and low air permeability favorable toair bags. For example, Japanese Patent Laid-Open No.41438/1989 says thata base fabric for air bags, which is composed of fiber filaments havinga tenacity of at least 8.5 g/d and a monofilament fineness of at most 3deniers, attains the above-mentioned object. Though silent on the typeof the base fabric, coated or non-coated one, it substantially relatesto abase fabric coated with an elastomer such as chloroprene rubber. Incase where the technique disclosed is applied to non-coated basefabrics, they could have high tenacity and could be compactly foldableto save the necessary housing space, but their air permeability couldnot be lowered satisfactorily.

[0006] On the other hand, Japanese Patent Laid-Open No. 201650/1992discloses a technique for producing a base fabric for air bags havinghigh tenacity and capable of being compactly folded to save the housingspace for it, for which are used polyamide multifilaments composed of aplurality of modified cross-section monofilaments each having a finenessof from 1.0 to 12 deniers and having a degree of cross-sectionmodification of from 1.5 to 7.0. However, the technique disclosed is tosatisfy only the requirements for coated base fabrics for air bags, butis still problematic in point of the air permeation through non-coatedbase fabrics, especially the air permeation therethrough at the seams.

[0007] A technique relating to non-coated base fabrics is described inJapanese Patent Laid-Open No. 252740/1995, which says that a base fabricfor non-coated air bags having low air permeability and capable of beingcompactly folded and housed in a limited small space is formed offlattened cross-section yarns having a degree of cross-section flatnessof at least 1.5. However, the air permeation through the base fabricproduced according to the technique disclosed is not lower than 0.3cc/cm²/sec under low pressure (124 Pa), and does not satisfy lower airpermeation recently required in the art.

[0008] On the other hand, dual-system inflators are being investigatedfor satisfying the US Act VMVSS208revised in 2000. These are to inflateair bags in two stages, through which the gas pressure in the secondstage inflation is larger than that through conventional inflators. Forthese, therefore, the base fabric for air bags is required to have lowerair permeability under high pressure than before, and is required not tocause yarn distortion and slippage from sewing threads at the seams(this is hereinafter referred to as seam distortion).

[0009] From this viewpoint, for example, Japanese Patent2,950,954discloses a non-coated base fabric made of yarn shaving a totalfineness of from 300 to 400 dtex, but this could not still solve theproblem of seam distortion in the base fabric. Japanese Patent Laid-OpenNo.2359/1996 discloses abase fabric for air bags, of which the warp/weftcover factor falls between 900 and 1400. In this, the residual oilcontent of the base fabric and the slip resistance thereof arespecifically defined. However, this could not still solve the problem ofseam distortion in the base fabric.

[0010] The present invention has been achieved as a result ofinvestigations to solve the problems in the prior art mentioned above.

[0011] Specifically, the object of the invention is to provide a basefabric for non-coated air bags which satisfies all the requirements ofhigh tenacity, low air permeability and compact foldabilityindispensable to airbags and which further satisfies the advancedrequirements of low air permeability under high pressure especially atthe seams, not causing seam distortion, so as to be suitable to air bagsfor high-pressure inflation, and also to provide fibers for air bags.

DISCLOSURE OF THE INVENTION

[0012] The base fabric for non-coated air bags of the invention has thefollowing essential constitution.

[0013] In the base fabric for non-coated air bags of the invention, boththe warp and the weft or either of them comprise synthetic fibermultifilaments of flattened cross-section monofilaments having a degreeof flatness of from 1.5 to 8.0 and having a monofilament fineness of atmoat 10 dtex and a total fineness of from 200 to 1000 dtex, and the basefabric satisfies all the following (1) to (3):

[0014] (1) its cover factor falls between 1700 and 2200;

[0015] (2) its air permeability under atmospheric pressure is at most0.1 cc/cm²/sec; and

[0016] (3) its air permeability under high pressure is at most 20cc/cm²/sec.

[0017] Preferred embodiments of the base fabric for non-coated air bagsof the invention are the following (a) to (e). Satisfying theseconditions, the base fabric is expected to get better results.

[0018] (a) After inflated, the air permeation through the base fabricunder high pressure is at most 50 cc/cm²/sec.

[0019] (b) The horizontal index, HI, of the synthetic fibermultifilaments is at least 0.75 in terms of the cosine of the angle atwhich the horizontal direction of the base fabric crosses the directionof the major axis of the cross section of each monofilament.

[0020] (c) The number of residual entanglements in the warp drawn out ofthe base fabric is at most 10/m.

[0021] (d) The residual oil content of the base fabric is at most 0.1 %by weight.

[0022] (e) The synthetic fiber multifilaments are of a polyamide havinga viscosity relative to sulfuric acid of at least 3.0.

[0023] The fibers for air bags of the invention have the followingessential constitution.

[0024] The fibers for air bags comprise synthetic fiber multifilamentsand satisfy all the following (4) to (7):

[0025] (4) the degree of flatness of each monofilament, which isindicated by the ratio of the length, a, of the largest major axis tothe length, b, of the largest minor axis, a/b, of the cross section ofthe monofilament, falls between 1.5 and 8.0;

[0026] (5) the degree of surface smoothness of each monof ilament in thedirection of the major axis of the cross section, which is indicated bythe ratio of the length, c, of the smallest minor axis to the length, b,of the largest minor axis, c/b, is at least 0.8;

[0027] (6) the monofilament fineness is at most 10 dtex; and

[0028] (7) the length, b, of the largest minor axis is at most 15 μm.

[0029] Satisfying the following conditions (f) and (g), the fibers forair bags of the invention are expected to get better results.

[0030] (f) After stretched under tension, the number of residualentanglements in the fibers is at most 15/m.

[0031] (g) The synthetic fiber multifilaments are of a polyamide havinga viscosity relative to sulfuric acid of at least 3.0.

BRIEF DESCRIPTION OF THE DRAWINGS

[0032]FIG. 1 is a graphic view showing the monofilament cross-sectionprofile of the synthetic fiber multifilaments that constitute the basefabric for non-coated air bags of the invention.

[0033]FIG. 2 is a schematic view showing a method for producing thepolyamide fibers for air bags of the invention.

[0034]FIG. 3 is a graphic view showing the cross-section profile of theorifice of the spinneret used herein for producing flattenedcross-section fibers.

BEST MODES OF CARRYING OUT THE INVENTION

[0035] The invention is described in detail hereinunder.

[0036] The total fineness of the synthetic fiber multifilaments thatconstitute the base fabric for non-coated air bags of the inventionindispensably falls between 200 and 1000 dtex, preferably between 200and 700 dtex. The base fabric that comprises synthetic fibermultifilaments having a total fineness of smaller than 200 dtex could becompactly folded to save the housing space for it, but it is unfavorablesince its tenacity is low and the air bags made of it will burst whilethey inflate or when the inflated air bags collide against drivers orpassengers. On the other hand, synthetic fiber multifilaments having atotal fineness of larger than 1000 dtex satisfy the tenacity and thesafety necessary for air bags, but could not satisfy another requirementof compact foldability necessary to the invention.

[0037] Air bags are designed in different ways, depending on the type ofthe automobiles and the site thereof in which they are installed, andthe total fineness of the synthetic fiber multifilaments that constitutethe base fabric for such air bags shall be suitably determined. Forexample, in ordinary sedans, it is desirable that the synthetic fibermultifilaments for air bags to be installed at the driver seat and thepassenger seat have a total fineness of from 300 to 500 dtex. The totalfineness of the multifilaments falling within the range satisfies boththe necessary tenacity of air bags that must withstand the high inflatorgas pressure to rapidly restrain drivers and passengers from beingdamaged in collision and the compact foldability thereof that must behoused in a relatively small space in the steering wheel at a driverseat or in the dashboard at a passenger seat.

[0038] On the other hand, side air bags to be installed at both sides ofa driver seat and a passenger seat are required to have high tenacity inorder that they withstand an inflator gas pressure which is generallyplanned high so as to rapidly restrain drivers and passengers from beingdamaged in flank collision. For these, therefore, it is desirable thatthe total fineness of the synthetic fiber multifilaments to constitutethe base fabric falls between 450 and 700 dtex.

[0039] Inflatable curtains are also required to be folded and housed ina limited small space. For the base fabric for these, therefore, thetotal fineness of the multifilaments preferably falls between 200 and500 dtex.

[0040] The monofilament fineness of the synthetic fiber multifilamentsthat constitute the base fabric for non-coated air bags of the inventionis indispensably at most 10 dtex, preferably at most 7 dtex, morepreferably at most 5 dtex. In general, base fabrics of fibers having asmaller monofilament fineness are more flexible, and they can be morecompactly folded and housed in a smaller space. With the reduction inthe monofilament fineness of the multifilaments that constitute the basefabric, the cover factor of the base fabric increases, and, as a result,the air permeation through the base fabric is lowered. Multifilamentshaving a monofilament fineness of larger than 10 dtex are unfavorable,since the base fabric comprising them could not be compactly folded andhoused in a small space and its air permeability is high, and, afterall, the base fabric is unsuitable to air bags.

[0041] Regarding the monofilament cross-section profile of themultifilaments, the degree of flatness of the monofilament, which isindicated by the ratio of the length, a, of the largest major axis tothe length, b, of the largest minor axis, a/b, of the cross section ofthe monofilament, indispensably falls between 1.5 and 8.0, preferablybetween 2.0 and 6.0. In case where the synthetic fiber multifilamentshaving the flattened cross-section profile as in the defined range arewoven into a base fabric, they are so aligned that the major axis of thecross section of each monofilament runs in the horizontal direction ofthe resulting base fabric owing to the general tension applied to allthe fibers while they are woven. As a result, the void space per theunit area of the base fabric is reduced, and the air permeability of thebase fabric is thereby reduced as compared with that of a base fabric ofround cross-section fibers having a fineness of the same level. In casewhere the air permeation of the same level as that through a base fabricof round cross-section fibers is taken into consideration for the basefabric of the flattened cross-section fibers, the necessary amount ofthe flattened cross-section fibers for the base fabric is lowered. Inother words, the flattened cross-section fibers as in the defined rangecan form abase fabric for airbags that satisfies both low airpermeability and compact fold ability to save the housing space for it.If, however, the degree of flatness of the flattened cross-sectionfibers is smaller than 1.5, the difference between the fibers andordinary round cross-section fibers is small, and the flattenedcross-section fibers could not satisfactorily exhibit their effect. Onthe other hand, if the degree of flatness of the flattened cross-sectionfibers is larger than 8.0, the effect of the fibers is saturated and isno more augmented. If so, in addition, high-tenacity fibers of highquality necessary for air bags, concretely those having a tenacity of atleast 6.5 cN/dtex are difficult to obtain, and, moreover, the flatfibers having such a large degree of flatness could not be smoothlywoven into fabrics, or that is, their workability into woven fabrics isextremely poor. For these reasons, such too much flattened fibers areunfavorable.

[0042] As so mentioned in the above, the synthetic fiber multifilamentsthat constitute the base fabric for non-coated air bags of the inventionare characterized in that the monofilaments all have a flattenedcross-section profile and are so aligned that the major axis of thecross section of each mono filament runs in the horizontal direction ofthe base fabric.

[0043] To quantitatively express it, a horizontal index (HI) is definedherein for the alignment of the monofilaments. The horizontal index, HIis indicated by the mean value of the cosine (hi) of the angle (Θ) atwhich the major axis of the flattened cross section of each monofilamentof the base fabric crosses the horizontal direction of the base fabric.Numerically, HI is represented by the following equation:

HI=(Σhi)/f

[0044] wherein hi cosΘ,

[0045] Θ is the angle at which the major axis of the flattened crosssection of each monofilament crosses the horizontal direction of thebase fabric, and

[0046] f is the number of monofilaments measured.

[0047] Preferably, the horizontal index HI of the base fabric thatcomprises the flattened cross-section fibers of the invention is atleast 0.75, more preferably at least 0.85, even more preferably at least0.90. With the horizontal index HI defined to fall within the range, thebase fabric ensures the intended good foldability to save the housingspace for it and the intended low air permeability as in the above, andtherefore attains the object of the invention.

[0048] The cover factor of the base fabric for non-coated air bags ofthe invention indispensably falls between 1700 and 2200, preferablybetween 1800 and 2100.

[0049] The cover factor is represented by:

(D1×0.9)^(½)×N1+(D2×0.9)^(½)×N2,

[0050] in which D1 (dtex) indicates the total fineness of the warp;

[0051] N1 (/2.54 cm) indicates the texture density of the warp;

[0052] D2 (dtex) indicates the total fineness of the weft; and

[0053] N2 (/2.54 cm) indicates the texture density of the weft.

[0054] If its cover factor is smaller than 1700, the mechanicalproperties of the base fabric are poor, and, in particular, the airpermeation (P_(H)) thereof under high pressure is high. If so, inaddition, the multifilaments constituting the base fabric are oftendistorted at the seams. As a result, the base fabric is unfavorable fornon-coated air bags, since the air bags made of it could not well serveas safety guards. On the contrary, if the cover factor of the basefabric is larger than 2200, or that is, if the texture density thereofis too high, it is unfavorable since the base fabric could not becompactly folded to save the housing space for it. If so, in addition,the necessary amount of the fibers for the base fabric increases, andthe base fabric is after all expensive.

[0055] Accordingly, the cover factor of the base fabric is significantlyrelated to the compact foldability thereof, and it is important that thecover factor of the base fabric for non-coated air bags of the inventionfalls within the suitable range as so defined in the above.

[0056] For the base fabric for non-coated air bags, it is necessary thatthe air permeation through it under low pressure, P_(L), is at most 0.1cc/cm²/sec, preferably at most 0.08 cc/cm²/sec. It is also necessarythat the air permeation through the base fabric under high pressure,P_(H), is at most 20 cc/cm²/sec, preferably at most 15 cc/cm²/sec.

[0057] P_(L) indicates a degree of air permeation measured according tothe method defined in JISL1096(6.27./MethodA). P_(H) indicates a degreeof air permeation measured as follows: Air having a controlled pressureof 19.6 KPa is made to run through a circular test piece having adiameter of 10 cm, and the amount of the air having passed through thetest piece is measured by the use of a laminar flow air permeationmeter.

[0058] P_(L) and P_(H) indicate the necessary characteristics of thebase fabric for air bags, or that is, they directly indicate theinflatablity of air bags. Having P_(L) and P_(H) each falling within thedefined range, air bags well serve as safety guards and attain theobject of the invention. If P_(L) and P_(H) are higher than 0.1cc/cm²/sec and 20 cc/cm²/sec, respectively, the air bags could notsmoothly inflate in collision and are therefore unfavorable since theyare useless for safety guards.

[0059] After stretched, the degree of air permeation through the basefabric under high pressure, P_(S), is preferably at most 50 cc/cm²/sec.With P_(S) falling within the range, the air bags made of the basefabric ensure safe protection of drivers and passengers since theinflated air bags well keep their inner pressure when drivers orpassengers have pushed in them.

[0060] P_(S) is measured as follows: A sample of the base fabric havinga length of 20 cm and a width of 15 cm is stretched under tension of1764 N at a pulling rate of 200 mm/min in the longitudinal direction.Air having a controlled pressure of 19.6 KPa is made to run through acircular part having a diameter of 10 cm in the center of the sample,and the amount of the air having passed through the circular part ismeasured by the use of a laminar flow air permeation meter.

[0061] Also preferably, the number of residual entanglements in the warpof the base fabric is at most 10/m. With residual entanglements fallingwithin the range, the base fabric can be prevented from being distortedat the seams. The number of residual entanglements in the warp issignificantly related to the above-mentioned horizontal index HI.Concretely, when the number of residual entanglements in the warp is notlarger than 10/m, HI of the base fabric tends to increase and the airpermeation through the base fabric is kept low.

[0062] Also preferably, the residual oil content of the warp and theweft of the base fabric is at most 0.1 % by weight. With the residualoil content falling within the range, the frictional force of themonofilaments that constitute the base fabric increases and the airpermeation through the base fabric especially at the seams is lowered.

[0063] Next described are the fibers for air bags of the invention.

[0064] The monofilament cross-section profile of the fibers for air bagsof the invention is flattened as in FIG. 1, differing from an ordinaryoval or diamond shape. The degree of flatness of the monofilament crosssection falls between 1.5 and 8.0, indicated by the ratio of a/b inwhich a is the length of the largest major axis and b is the length ofthe largest minor axis of the cross section. The cross-section profileis formed by aligning plural circles in a line, for which the diameterof each circle corresponds to the minor axis of the cross section.

[0065] Regarding the monofilament cross-section profile, the degree ofsurface smoothness of each monofilament in the direction of the majoraxis of the cross-section, which is indicated by the ratio of thelength, c, of the smallest minor axis to the length, b, of the largestminor axis, c/b, is indispensably at least 0.8, preferably at least0.85. With the degree of surface smoothness falling within the range,the frictional force of the monofilaments increases and the airpermeation through the base fabric for air bags made of the fibers iswell lowered. If fibers having a degree of surface smoothness of smallerthan 0.8 are formed into a base fabric for air bags, the air permeationthrough the base fabric, especially at the seams could not be lowered,and therefore the fibers are not suitable for air bags intended in theinvention.

[0066] Indispensably in the invention, the length, b, of the largestminor axis is at most 15 μm, and the monofilament fineness is at most 10dtex. With the length, b, of the largest minor axis and the monofilamentfineness falling within the range, the fibers are favorable to the basefabric for non-coated air bags intended in the invention.

[0067] The constitutive components of the fibers for air bags of theinvention are not specifically defined. For ensuring high tenacity andgood flexibility favorable to air bags, polyamide having a viscosityrelative to sulfuric acid of at least 3.0 is preferred for the fibers.The polyamide may be either a homopolymer or a copolymer, and it maycontain inorganic substances such as titanium oxide, silicon oxide andcalcium carbonate, and also other chemicals such as weather-proofingagent and antioxidant, for improving the color, the weather resistanceand the oxidation resistance of the polymer fibers.

[0068] Next described is a method for producing the fibers for air bagsof the invention.

[0069] The fibers for air bags of the invention can be produced in anyordinary melt-spinning method. FIG. 2 shows one example of the methodfor producing polyamide fibers for air bags.

[0070] As illustrated, the yarn (Y) having been spun out through thespinning pack (0) in a melt-spinning machine is led to pass through theheating zone (1) disposed just below the spinneret. Preferably, thelength of the heating zone (1) falls between 100 and 200 mm. Havingpassed through the heating zone of which the length is defined to fallwithin the range, the fibers can readily have the desired tenacity andthe desired degree of flatness favorable to air bags intended in theinvention. Next, the yarn (Y) is cooled and solidified by the chill airthat is blowing at a speed of 20 to 50 m/min in the chilling zone (2).Then, after having passed through the spinning duct (3), the yarnreceives oil from the oil supply unit (4), and then taken up by the spunyarn-taking up rollers (5) and (6).

[0071] Next, the yarn (Y) is led to run along the hot rollers (7), (8)and (9) each running at a high speed, in that order and is thus drawn bythese rollers. For further increasing their tenacity, the fibers arepreferably drawn in two or more stages. Next, the yarn is wound aroundthe rollers (10) and relaxed therearound, and then led to the controlguides (12, 12′) and the entangling unit (11) in which it is entangled.With that, the yarn is wound up in the winder (13). The relaxation isimportant for determining the shrink property of the fibers obtained. Ingeneral, the fibers are relaxed to a degree of from 3 to 15 in orderthat they have a desired degree of shrinkage favorable to air bags.After stretched, the fibers are entangled to have at most 15entanglements/m, for which pressure air of from 0.05 to 0.4 MPa ispreferably applied to the fibers in the entangling unit.

[0072]FIG. 3(A) shows the cross-section profile of the orifice of thespinneret usable for obtaining the flattened cross-section fibers of theinvention. Regarding the structure of the spinneret orifice, the roundparts (d) at both ends and in the inside between them are connected in aline via the slit parts (e). For efficiently obtaining the flattenedcross-section fibers of the invention that satisfy the monofilamentfineness, the degree of flatness, the degree of surface smoothness inthe direction of the major axis of the cross section and the length ofthe major axis of the cross section defined herein, it is desirable thatthe number of the round parts (d) is at least 2, the diameter of eachround part falls between 0.15 and 0.25 mm, the width of the slit (e)falls between 0.10 and 0.20 mm, and the length of the slit falls between0.10 and 0.20 mm. The orifice profile of FIG. 3(B) is undesirable, sincethe surface smoothness in the direction of the major axis of the crosssection of the fibers produced through it could not satisfy therequirement defined herein and the air permeation through the basefabric for air bags made of the fibers could not be low.

[0073] For producing the base fabric for non-coated air bags of theinvention, or that is, for weaving the base fabric from the fibers ofthe invention, usable are a water-jet loom, a rapier loom, an air-jetloom, etc. The residual oil content of the base fabric for non-coatedairbags of the invention is preferably at most 0.1 % by weight. Forweaving the base fabric from the fibers, therefore, preferably used is awater-jet loom as facilitating the oil removal from the fibers. Alsopreferably, the tension of the warp falls between 0.2 and 0.6 cN/dtex inthe process of weaving the fabric. Under the tension falling within therange, the flattened cross-section fibers are well woven into theintended base fabric and are favorably aligned in the woven fabric, orthat is, the horizontal index HI of the fibers constituting the wovenfabric well meets the requirement defined herein and the airpermeability of the woven fabric can be lowered. After having been thuswoven, the base fabric is preferably scoured and/or thermally set at 160to 190° C.

[0074] The embodiments of the invention have been described in detailhereinabove. The base fabric made of the flattened cross-section fibersof the invention is characterized in that it is favorable to air bags,especially to non-coated air bags. Specifically, the base fabricfavorable to such air bags of the invention is characterized in that itsair permeability is low, especially at the seams, and it is compactlyfoldable to save the housing space for it. These characteristics of thebase fabric of the invention result from the flattened cross-sectionfibers that constitute the base fabric. The significant featurescharacteristic of the fibers are described below.

[0075] As mentioned hereinabove, (1) in the base fabric of flattenedcross-section fibers of the invention, the monofilaments of the fibersare so aligned that the major axis of the cross section of eachmonofilament runs in the horizontal direction of the woven fabric.Therefore, the cover factor of the base fabric is high and the airpermeability thereof is low. In addition, the base fabric is compactlyfoldable to save the housing space for it, and it is thin and flexible.Moreover, (2) the cross section of each monofilament of the flattenedcross-section fibers of the invention is a rectangular cross section.Specifically, it is a flattened cross section that is formed by aligningplural circles in a line, for which the diameter of each circlecorresponds to the minor axis of the cross section. The length of theminor axis is at most 15 μm. For example, when the length of the minoraxis is 10 μm, falling within the preferred range thereof, the finenessof the monofilament corresponds to 1 denier (1.1 dtex) and falls in thecategory of microfibers. In the base fabric of the invention, theflattened cross-section fibers that are considered to fall in thecategory of microfibers are aligned in the horizontal direction of thebase fabric, and, as a result, the base fabric of the invention can becompactly folded to save the housing space for it, and it is thin andflexible. Accordingly, the base fabric of the invention is comparable toordinary base fabrics of microfibers in point of the texture. Basefabrics of microfibers are known for air bags, but it is difficult tostably spin microfibers in a direct spinning process. On the other hand,microfibers produced in a process of sea/island polymer alignment areexpensive and could not be put into practical use.

[0076] For air bags, the base fabric of the invention is superior to anyother conventional base fabrics made of ordinary fibers of thinnedmonofilaments, since its air permeability is low, it is compactlyfoldable to save the housing space for it, and it is thin and flexible.Moreover, the base fabric of the invention can be readily produced inany ordinary melt-spinning process or direct spinning and drawingprocess, and its practicability is significant.

EXAMPLES

[0077] The invention is described more concretely with reference to thefollowing Examples and Comparative Examples. The physical propertiesreferred to in the specification and in the following Examples aremeasured according to the methods mentioned below.

[0078] [Fineness]

[0079] Measured according to JIS L-1013.

[0080] [Tenacity, Elongation]po Measured according to JISL-1013. Thelength of the sample tested is 25 cm, and the pulling rate is 30 cm/min.

[0081] [Viscosity relative to sulfuric acid]po 2.5 g of a sample to betested is dissolved in 25 cc of 96 % sulfuric acid, and its viscosity ismeasured at a constant temperature of 25° C. in a thermostat, using anOstwaldviscometer. [Degree of flatness]

[0082] On the optical microscopic picture (×200) of a sample to betested, the cross section of each monofilament is analyzed. The length,a, of the largest major axis in the direction of the major axis of thecross section; and the length, b, of the largest minor axis in thedirection of the minor axis of the cross section are measured. The dataof ten monofilaments thus measured are averaged, from which the degreeof flatness is obtained according to the following equation:

Degree of Flatness=a/b

[0083] [Horizontal index, HI]

[0084] On the optical microscopic picture (×200) of a sample to betested, like that taken for the measurement of the degree of flatness asabove, the angle Θ at which the major axis of the cross section of eachflattened cross-section fiber crosses the horizontal direction of thebase fabric is measured. Based on the mean value of the cosine of theangle thus measured, the horizontal index, HI, is obtained according tothe following equation. The number of the monofilaments measured, f=100.

HI=(Σhi)/f

[0085] wherein hi=cosΘ,

[0086] Θ is the angle at which the major axis of the flattened crosssection of each monofilament crosses the horizontal direction of thebase fabric, and

[0087] f is the number of the monofilaments measured.

[0088] [Surface smoothness]

[0089] On the optical microscopic picture (×200) of a sample to betested, the cross section of each monofilament is analyzed. The length,b, of the largest minor axis and the length, c, of the smallest minoraxis in the direction of the minor axis of the cross section aremeasured. The data of ten monofilaments thus measured are averaged, fromwhich the degree of surface smoothness is obtained according to thefollowing equation:

Degree of Surface Smoothness=c/b

[0090] [Number of residual entanglements, and the number ofentanglements after stretching treatment]

[0091] For measuring the number of the residual entanglements in a basefabric, each one of the warp is nipped and drawn out of the base fabric,at an angle of from 20 to 450 relative to the direction of the warp andat a pulling rate of from 40 to 60 sec/m or so. The number of theentanglements/meter in the thus-drawn warp is measured in a method ofdipping the sample in a water bath. 10 samples are measured, and thedata are averaged to obtain the number of the entanglement/m of thewarp. The water bath has a length of 70 cm, a width of 15 cm and a depthof 5 cm. This is partitioned at 10 cm from each end in the longitudinaldirection, and filled with pure water to a depth of about 3 cm. Toremove the influence of impurities such as oil on the measurement, thepure water in the bath is exchanged for fresh one in every measurement.

[0092] For measuring the number of entanglements after stretched, thefiber sample having a length of 1.0 m is stretched by applying a load of2 cN/dtex thereto for 5 seconds, and after the load has been removed,the sample is measured in a water bath according to the same method asabove.

[0093] [Residual oil content]

[0094] The warp and the weft are individually drawn out of a base fabricin the same manner as that for the measurement of the residualentanglements as above, and the samples are measured according to JISL-1096 (6.36.1 Method A) (alcohol/benzene extraction method). Thedetails are as follows: About 5 g of a sample piece is prepared, and itsweight is accurately measured. This is lightly pushed into a Soxhletextractor, not using a cylindrical paper filter therein, and 120 ml of amixture of alcohol/benzene (½ by volume) is put into the accessory flaskattached to the extractor. With that, the flask is heated for 3 hours ina water bath, and the solution formed in the sample section in theextractor is returned to the flask. The contents of the flask areconcentrated to about 3 ml, and moved to a balance bottle. The bottle isput in a water bath, and the solvent is evaporated away. The absolutedry weight of the residue is measured. The same test is repeated twotimes.

[0095] The residue obtained according to the method of JIS L-1096(3.36.1 Method A) is collected, and the monomer/oligomer content (% byweight) of the polyamide in the residue is measured through gaschromatography and high-performance liquid chromatography. For thequantification standards, used are adipic acid and hexamethylenadipamide(special-grade chemicals from Tokyo Chemical) and nylon 66 cyclic trimer(produced by Toray).

[0096] The data obtained in the two tests are averaged, and the oilcontent of the sample is obtained according to the following equation.

Oil Content ×(data in alcohol/benzene extraction)−(data inmonomer/oligomer analysis).

[0097] [Tensile strength of base fabric]

[0098] Measured according to JIS L-1096 (6.12.1 Method A).

[0099] [Tear strength of base fabric]

[0100] Measured according to JIS L-1096 (6.15.2 Method A-2).

[0101] [Cover factor]Represented by:

(D1×0.9)^(½)×N1+(D2×0.9)^(½)×N2,

[0102] in which D1 (dtex) indicates the total fineness of the warp;

[0103] N1 (/2.54 cm) indicates the texture density of the warp;

[0104] D2 (dtex) indicates the total fineness of the weft; and

[0105] N2 (/2.54 cm) indicates the texture density of the weft.

[0106] [Air permeability under low pressure, P_(L)]

[0107] Measured according to JIS L-1096 (6.27.1 Method A).

[0108] Its details are as follows: A base fabric to be tested is cut toprepare its sample having a length of 20 cm and a width of 15 cm. Airhaving a controlled pressure of 124 Pa is made to run through a circularpart having a diameter of 10 cm of the sample, and the amount of the air(cc/cm²/sec) having passed through the circular part is measured by theuse of a laminar flow air permeation meter.

[0109] [Air permeability under high pressure, P_(H)]

[0110] A base fabric to be tested is cut to prepare its sample having alength of 20 cm and a width of 15 cm. Air having a controlled pressureof 19.6 KPa is made to run through a circular part having a diameter of10 cm of the sample, and the amount of the air (cc/cm²/sec) havingpassed through the circular part is measured by the use of a laminarflow air permeation meter.

[0111] [Air permeability after stretched, P_(S)]

[0112] A base fabric to be tested is cut to prepare its sample having alength of 20 cm and a width of 15 cm. The sample is stretched undertension of 1764 N at a pulling rate of 200 mm/min in the longitudinaldirection. Air having a controlled pressure of 19.6 KPa is made to runthrough a circular part having a diameter of 10 cm of the sample, andthe amount of the air (cc/cm²/sec) having passed through the circularpart is measured by the use of a laminar flow air permeation meter.

[0113] [Air permeability at seams]

[0114] Using a sewing machine, Juki Corporation's MH-380 Model, twosheets of a base fabric to be tested, each having a length of 20 cm anda width of 20 cm, are sewed with sewing thread of 1400 dtex in a mode ofmulti-thread chain stitch, with leaving a margin of 2 cm to sew up them.The needle used is TV×7#19; the sewing pitch is 3 mm; and the distancebetween the two stitch lines is 2 mm. Air having a controlled pressureof 19.6 KPa is made to run through a circular part having a diameter of10 cm in the center of the sample with the seams, and the amount of theair (cc/cm²/sec) having passed through the circular part is measured bythe use of a laminar flow air permeation meter.

[0115] [Seam distortion]

[0116] Two sheets of a base fabric to be tested are prepared, eachhaving a length of 7 cm and a width of 7 cm. With one on top of theother so that the warp and the weft are individually in the samedirection in the two, these are sewed in a mode of multi-thread chainstitch. The margin left to sew up them is 2.5 cm; the needle thread andthe bobbin thread used are both of nylon 6.6 1400 dtex/one; the sewingmachine used is Juki Corporation's MH-380 Model; and the needle used isTV×7#19. The thus-sewed sample is set in a tensile tester, in which itis held by a chuck of 5 cm wide with a margin of 1 cm left at both ends.In that condition, an elastic stress of 1274 N is applied to the sample,and the length of the gap having appeared between the base fabric andthe sewing thread is read with a measure. Large five gaps are thusmeasured, and the data are averaged.

[0117] [Thickness of base fabric]

[0118] A base fabric to be tested is sewed up to form an air bag havinga volume of 60 liters. This is bellows-wise folded four times both inthe opposite horizontal directions and then four times both in theopposite vertical directions. Having thus folded, this has an area of150×150 cm. A load of 4000 g is applied to this, and the thickness ofthe thus-folded bag is measured.

[0119] [Examples 1 to 13]

[0120] Using an extruder-type spinning machine, nylon 66 chips having aviscosity, relative to 98 % sulfuric acid at 25° C., of 3.7 weremelt-spun at 295° C.

[0121] Precisely, the nylon melt was spun out of a spinning pack with aspinneret having an orifice profile as in Table 1; then led to passthrough a hot zone disposed just below the spinneret (the hot zone washeated at 230° C. and had a length of 150 mm); then cooled andsolidified in a chilling zone with chill air blowing at a speed of 30m/min; then lubricated with an oiling roller; then wound around atake-up roll, a feed roll, a first stretch roll, a second stretch rolland a tension control roll in that order to thereby draw the fibers intwo stages to a total draw ratio of 4.1 times; then relaxed by 7 %; andfinally wound up in a winder at a speed of 3800 m/min. After relaxed,the fibers were entangled with pressure air of 0.3MPa applied thereto inan entangling unit. The physical properties of the synthetic fibermultifilaments for air bags, thus produced according to the process asabove, are shown in Table 1. TABLE 1 Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6Ex. 7 Ex. 8 Spinneret rounded, diameter (mm) 0.20 0.20 0.15 0.20 0.150.20 0.20 0.20 Orifice number of sections (−) 5 3 5 5 5 5 5 5 Profileslit, width (mm) 0.10 0.10 0.10 0.10 0.10 0.10 0.10 0.10 length (mm)0.10 0.10 0.20 0.10 0.10 0.10 0.10 0.10 467 Total fineness (dtex) 467467 467 467 467 467 467 467 Number of filaments (−) 96 96 96 72 144 9696 96 Monofilament fineness (dtex) 4.86 4.86 4.86 6.49 3.24 4.86 4.864.86 Degree of flatness (−) 3.60 2.21 5.51 3.42 3.48 3.60 3.60 3.60Degree of surface smoothness (−) 0.97 0.97 0.93 0.96 0.97 0.97 0.97 0.97Length of largest minor axis (μm) 10 13 8 13 9 10 10 10 Tenacity(cN/dtex) 7.92 7.86 7.68 7.95 7.72 7.92 7.92 7.92 Elongation (%) 22.123.0 20.4 23.9 21.1 22.1 22.1 22.1 Shrinkage in boiling water (%) 6.26.2 6.1 6.3 6.2 6.2 6.2 6.2 Number of entangled after 10 10 12 9 13 1010 10 stretched (/m) Ex. 9 Ex. 10 Ex. 11 Ex. 12 Ex. 13 Ex. 14 Spinneretrounded, diameter (mm) 0.20 0.20 0.20 0.20 0.20 0.20 Orifice number ofsections (−) 5 4 5 5 5 5 Profile slit, width (mm) 0.10 0.10 0.10 0.100.10 0.10 length (mm) 0.10 0.20 0.10 0.10 0.10 0.10 Physical Totalfineness (dtex) 467 467 467 350 700 467 Properties Number of filaments(−) 96 96 96 72 144 96 of Fibers Monofilament fineness (dtex) 4.86 4.864.86 4.86 4.86 4.86 Degree of flatness (−) 3.58 3.54 3.51 3.58 3.39 3.60Degree of surface smoothness (−) 0.96 0.92 0.96 0.94 0.95 0.97 Length oflargest minor axis (μm) 10 10 10 10 11 10 Tenacity (cN/dtex) 7.67 7.887.68 7.96 8.08 7.92 Elongation (%) 20.5 23.4 24.6 23.5 23.4 22.1Shrinkage in boiling water (%) 6.2 6.3 9.0 6.2 6.1 6.2 Number ofentangled after 14 10 10 10 8 10 stretched (/m)

[0122] Next, the resulting synthetic fiber multifilaments were warpedunder tension of 0.3 cN/dtex at a speed of 200 m/min, and then woveninto a fabric by the use of a water-jet loom (Tsudakoma's ZW303) drivingat a revolution speed of 800 rpm. Next, the thus-woven fabric wasscoured by dipping it in a hot water bath at 80° C. that contained 0.5g/liter of sodium alkylbenzenesulfonate and 0.5 g/liter of soda ash, for3 minutes, followed by drying it in an atmosphere at 130° C. for 3minutes. Finally, this was thermally set at 180° C. for one minute toobtain a base fabric for air bags.

[0123] The base fabric for non-coated air bags obtained according to theprocess as above was analyzed and tested for the texture density (countof warp/weft) and for the properties thereof. The data are in Table 2.TABLE 2 Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6 Ex. 7 Ex. 8 PropertiesTexture density (warp/weft) 48/48 48/48 48/48 48/48 48/48 45/53 51/5153/53 of Base (/2.54 cm) Fabric Cover factor (−) 1967 1967 1967 19671967 1844 2090 2172 Air Permeability (cc/cm²/sec) under low pressure(124 Pa) 0.02 0.04 0.02 0.05 0.02 0.08 0.01 0.01 under high pressure(19.6 KPa) 11 15 8 14 9 19 6 6 after stretched (19.6 KPa) 23 37 21 31 1942 15 12 at the seams (19.6 KPa) 21 26 19 28 19 29 11 9 Seam distortion(mm) 1.2 1.5 1.1 1.3 1.1 1.7 1.1 0.9 Thickness of base fabric (mm) 0.270.27 0.27 0.27 0.26 0.24 0.29 0.32 Tensile strength (N/cm) 620 624 618624 626 580 639 668 Tear strength (N) 197 201 187 210 187 168 211 219Number of residual entanglements 4 3 4 4 5 3 4 4 (/m) Horizontal index(−) 0.95 0.94 0.96 0.94 0.92 0.95 0.95 0.94 Residual oil content of base0.02 0.03 0.03 0.03 0.04 0.03 0.04 0.06 fabric (%) Ex. 14 not Ex. 9 Ex.10 Ex. 11 Ex. 12 Ex. 13 scoured Properties Texture density (warp/weft)48/48 48/48 48/48 48/48 48/48 45/45 of Base (/2.54 cm) Fabric Coverfactor (−) 1967 1967 1967 1967 1967 1844 Air Permeability (cc/cm²/sec)under low pressure (124 Pa) 0.02 0.02 0.04 0.01 0.02 0.03 under highpressure (19.6 KPa) 11 12 14 8 10 12 after stretched (19.6 KPa) 34 25 1718 26 29 at the seams (19.6 KPa) 30 23 15 23 20 27 Seam distortion (mm)1.7 1.7 0.9 1.1 1.4 1.5 Thickness of base fabric (mm) 0.27 0.27 0.270.24 0.36 0.27 Tensile strength (N/cm) 613 620 611 533 772 621 Tearstrength (N) 217 200 187 168 288 211 Number of residual entanglements 64 4 3 4 5 (/m) Horizontal index (−) 0.93 0.95 0.95 0.95 0.94 0.94Residual oil content of base 0.08 0.03 0.04 0.05 0.05 0.10 fabric (%)

[0124] [Example 14]

[0125] In the same manner as in Example 1, fibers for air bags wereproduced, and these were woven and thermally set to give a base fabricfor non-coated air bags. In this, however, the woven fabric was notscoured. Table 1 shows the orifice profile of the spinneret used and thephysical properties of the fibers produced; and Table 2 shows theproperties of the base fabric produced.

[0126] [Comparative Examples 1 to 5]

[0127] Fibers for air bags were produced in the same manner as inExample 1, for which, however, the orifice profile of the spinneret usedis as in Table 3. The physical properties of the synthetic fibers forair bags obtained are in Table 3. TABLE 3 Co. Ex. 1 Co. Ex. 2 Co. Ex. 3Co. Ex. 4 Co. Ex. 5 Co. Ex. 6 Co. Ex. 7 Co. Ex. 8 Spinneret rounded,diameter (mm) 0.30 0.20 — 0.30 0.30 0.20 0.20 0.20 Orifice number ofsections (−) 1 5 — 3 2 5 5 5 Profile slit, width (mm) — 0.10 0.20 0.100.10 0.10 0.10 0.10 length (mm) — 0.10 1.40 0.20 0.80 0.10 0.10 0.10Physical Total fineness (dtex) 467 467 467 467 467 467 467 467Properties Number of filaments (−) 96 96 96 96 96 96 96 96 of FibersMonofilament fineness (dtex) 4.86 4.86 4.86 4.86 4.86 4.86 4.86 4.86Degree of flatness (−) 1.00 3.61 3.33 3.41 3.46 3.61 3.56 3.60 Degree ofsurface smoothness (−) (circular 0.97 (oval 0.71 0.74 0.97 0.97 0.97cross cross section) section) Length of largest minor axis (μm) (23) 10(11) 10 10 10 10 10 Tenacity (cN/dtex) 8.03 7.92 8.02 7.91 7.89 7.927081 7.92 Elongation (%) 24.3 22.1 22.2 23.2 21.2 22.1 22.0 22.1Shrinkage in boiling water (%) 6.2 6.2 6.1 6.2 6.2 6.2 6.2 6.2 Number ofentangled after 10 10 10 10 10 10 20 10 stretched (/m)

[0128] Next, the resulting synthetic fiber multifilaments were woven,scoured and thermally set to give a base fabric for non-coated air bags,also in the same manner as in Example 1. The properties of the basefabric thus obtained are in Table 4. TABLE 4 Co. Ex. 8 not scoured, Co.Ex. 7 and not not thermally Co. Ex. 1 Co. Ex. 2 Co. Ex. 3 Co. Ex. 4 Co.Ex. 5 Co. Ex. 6 scoured set Properties Texture density (warp/weft) 48/4855/55 48/48 48/48 48/48 48/48 48/48 48/48 of Base (/2.54 cm) FabricCover factor (−) 1967 2255 1967 1967 1967 1967 1967 1967 AirPermeability (cc/cm²/sec) Under low pressure (124 Pa) 0.23 0.03 0.160.02 0.02 0.15 0.12 0.06 Under high pressure (19.6 KPa) 65 11 30 12 1132 22 16 After stretched (19.6 KPa) 96 24 72 55 59 47 57 53 At the seams(19.6 KPa) 81 20 62 33 35 33 38 35 Seam distortion (mm) 2.5 1.9 2.1 1.92.1 2.3 1.8 1.9 Thickness of base fabric (mm) 0.29 0.37 0.28 0.27 0.270.28 0.27 0.27 Tensile strength (N/cm) 623 745 614 623 616 612 613 612Tear strength (N) 210 250 192 193 199 192 191 189 Number of residualentanglements 2 1 4 4 4 9 13 3 (/m) Horizontal index (−) — 0.94 0.870.96 0.95 0.72 0.84 0.93 Residual oil content of base 0.04 0.06 0.040.04 0.03 0.05 0.20 0.15 fabric (%)

[0129] [Comparative Example 6]

[0130] In the same manner as in Example 1, fibers for air bags and abase fabric for non-coated air bags were produced. In this, however, thefibers produced were warped under tension of 0.1 cN/dtex, and thenwoven. Table 3 shows the orifice profile of the spinneret used and thephysical properties of the fibers produced; and Table 4 shows theproperties of the base fabric produced.

[0131] [Comparative Examples 7 and 8]

[0132] In the same manner as in Example 1, fibers for air bags wereproduced, and these were woven into a base fabric for non-coated airbags. In Comparative Example 7, however, the woven fabric was notscoured; and in Comparative Example 8, the woven fabric was neitherscoured nor thermally set. Table 3 shows the orifice profile of thespinneret used and the physical properties of the fibers produced; andTable 4 shows the properties of the base fabric produced.

[0133] As in Table 1 to Table 4, the base fabrics for non-coated airbags of the invention are all superior to the conventional base fabricsin point of the high tenacity thereof, the low air permeability thereofunder low pressure, under high pressure, after stretched and at theseams, the small thickness thereof, and the compact foldability thereofto save the necessary housing space. The base fabrics for non-coated airbags of the invention satisfy all the requirements for air bags.

Industrial Applicability

[0134] As described hereinabove, the base fabric for non-coated air bagsof the invention has the necessary properties of high tenacity, low airpermeability and compact foldability to save the housing space for it,and is favorable to air bags for high-pressure inflation. The syntheticfiber multifilaments to constitute the base fabric for air bags of theinvention can be readily produced in any ordinary melt-spinning processor direct spinning and drawing process, and any ordinary weaving machinecan be used in weaving them into base fabrics. To that effect, thepracticability of the invention is significant.

1. A base fabric for non-coated air bags in which both the warp and theweft or either of them comprise synthetic fiber multifilaments offlattened cross-section monofilaments having a degree of flatness offrom 1.5 to 8.0 and having a monofilament fineness of at moat 10 dtexand a total fineness of from 200 to 1000 dtex, and which satisfies allthe following (1) to (3): (1) its cover factor falls between 1700 and2200; (2) its air permeability under low pressure, P_(L), is at most 0.1cc/cm²/sec; and (3) its air permeability under high pressure, P_(H), isat most 20 cc/cm²/sec.
 2. The base fabric for non-coated air bags asclaimed in claim 1, of which the air permeability under high pressureafter stretched, P_(S), is at most 50 20 cc/cm²/sec.
 3. The base fabricfor non-coated air bags as claimed in claim 1 or 2, wherein thehorizontal index, HI, of the synthetic fiber multifilaments is at least0.75 in terms of the cosine of the angle at which the horizontaldirection of the base fabric crosses the direction of the major axis ofthe cross section of each monofilament.
 4. The base fabric fornon-coated air bags as claimed in any one of claims 1 to 3, which issuch that the number of residual entanglements in the warp drawn out ofthe base fabric is at most 10/m.
 5. The base fabric for non-coated airbags as claimed in any one of claims 1 to 4, of which the residual oilcontent is at most 0.1 % by weight.
 6. The base fabric for non-coatedair bags as claimed in any one of claims 1 to 5, wherein the syntheticfiber multifilaments are of a polyamide having a viscosity relative tosulfuric acid of at least 3.0.
 7. Fibers for air bags, which comprisesynthetic fiber multifilaments and satisfy all the following (4) to (7):(4) the degree of flatness of each monofilament, which is indicated bythe ratio of the length, a, of the largest major axis to the length, b,of the largest minor axis, a/b, of the cross section of themonofilament, falls between 1.5 and 8.0; (5) the degree of surfacesmoothness of each monofilament in the direction of the major axis ofthe cross section, which is indicated by the ratio of the length, c, ofthe smallest minor axis to the length, b, of the largest minor axis,c/b, is at least 0.8; (6) the monofilament fineness is at most 10 dtex;and (7) the length, b, of the largest minor axis is at most 15 μm. 8.The fibers for air bags as claimed in claim 7, in which the number ofresidual entanglements after stretched under tension is at most 15/m. 9.The fibers for air bags as claimed in claim 7 or 8, of which thesynthetic fiber multifilaments are of a polyamide having a viscosityrelative to sulfuric acid of at least 3.0.
 10. The base fabric fornon-coated air bags as claimed in any one of claims 1 to 6, whichcomprises the fibers of any of claims 7 to 9.